Heating for a printing drum

ABSTRACT

A printing drum for a liquid electrophotographic printing system which comprises a photosensitive surface and a heating device mounted to the printing drum. The heating device heats the photosensitive surface of the printing drum to a predetermined temperature.

BACKGROUND

The description is related to a heating device of a printing drum in aliquid electrophotographic (LEP) printing system.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of examples will be described, by way of example, in thefollowing detailed description with reference to the accompanyingdrawings in which like reference numerals correspond to similar, thoughperhaps not identical, components. For the sake of brevity, referencenumerals or features having a previously described function may or maynot be described in connection with other drawings in which they appear.

Non-limiting examples will now be described with reference to theaccompanying drawings, in which:

FIG. 1 shows a simplified perspective view of a cut-open example of aprinting drum of a LEP printing system.

FIG. 2 shows a simplified front view of an example of the printing drumof a LEP printing system.

FIG. 3 shows a simplified front view of a further example of theprinting drum of a LEP printing system.

FIGS. 4 a - 4 c show a simplified perspective view of a mountingarrangement of an example printing drum of a LEP printing system.

FIG. 5 shows a simplified perspective view of an example of the printingdrum of a LEP printing system comprising a temperature sensor.

FIG. 6 shows a simplified perspective view of an example of the printingdrum of a LEP printing system comprising electrical connections.

FIG. 7 shows a simplified front view of two example printing drums, withone printing drum engaged with an intermediate member of a LEP printingsystem.

FIG. 8 shows a simplified front view of an example LEP printing systemwith an example printing drum.

FIG. 9 - FIG. 13 show examples of a method to enhance the print qualityof a photosensitive surface of a printing drum in a LEP printing system.

The figures are not necessarily to scale, and the size of some parts maybe exaggerated to more clearly illustrate the example shown. Moreover,the drawings provide examples and/or implementations consistent with thedescription; however, the description is not limited to the examplesand/or implementations provided in the drawings.

DETAILED DESCRIPTION

In some printing systems, a latent print image may be generated on theexterior of a printing drum. A print agent may be applied to the latentprint image to create a print image. The print image may then betransferred to substrate to create a printed image.

For example, a liquid electrophotographic (LEP) printing system maycomprise a printing drum with a photosensitive surface on which a printimage may be created as described herein. The photosensitive surface maybe uniformly charged by a photoconductor charging unit, before a writinghead selectively discharges pixels of the photosensitive surface to forma latent electrostatic image. A print agent may be attracted to orrepelled from a pixel of the latent electrostatic image depending on theelectrostatic potential of the respective pixel to create a print image.The resulting print image is then transferred to a substrate to create aprinted image.

In some examples, an intermediate member transfers the print image fromthe photosensitive surface of the printing drum to the substrate. Theintermediate member is heated to melt and blend print agent particlesinto a smooth film. Hence, the print image may be defined on theintermediate member. Upon contact with the cooler substrate, the printimage solidifies and the printed image is generated. In other examples,where the print image is directly transferred to substrate, thesubstrate may be heated to permanently fuse and dry the print image.

In some example LEP printing systems, the intermediate member has atemperature during operation considerably higher than, for instance,ambient temperature, such that the print agent particles are heated andmelted. In some LEP printing systems, heating the intermediate membere.g. after a break or standby, may present a time bottleneck in theoverall printing process.

In various LEP printing systems, the intermediate member to transfer inkto media is a belt. In other LEP printing systems, the intermediatemember is a blanket, a blanket belt or a drum. In some examples, theprint image is transferred by contact to the substrate. In otherexamples, the print image is transferred to the substrate via anelectric field. The substrate may in principle comprise any material,including paper, card, plastics, or fabric.

The print agent may comprise ink, toner, coating and the like. The inkmay be powdered or liquid, such as liquid ink. The liquid ink maycontain a carrier liquid, such as imaging oil, and ink particles whichare pigments that are encapsulated by a resin. The electrostaticallycharged photosensitive surface of the printing drum controls placementof the ink particles.

In various LEP printing systems, the photosensitive surface of theprinting drum may provide a predetermined temperature distribution forthe development of the print agent. In some examples, the predeterminedtemperature distribution may be uniform. In other examples, thepredetermined temperature distribution may be non-uniform. Thistemperature distribution may on average be higher than the ambienttemperature of the LEP printing system.

During a printing process, the photosensitive surface of the printingdrum may experience unfavorable heat loss which could hinder theachievement of the predetermined temperature distribution. The heat lossmay be higher at the lateral ends of the printing drum than, forinstance, at the middle part of the printing drum. This may beattributed to endcaps which may close the printing drum at lateral endsand which may have a relatively high heat capacity. Various LEP printingsystems may provide a number of different printing job formats. Hence,the predetermined temperature distribution may also be based on thedimensions of the printing job.

In some examples, a bi-product may be accumulated on the photosensitivesurface of the printing drum. This bi-product may be accumulated duringone or several printing processes. This bi-product, also known as“oxidized imaging oil”, may comprise residual imaging oil, ink particlesor other contaminations. The oxidized imaging oil may experienceoxidation when exposed to the photoconductor charging unit and remainchemically attached to the photosensitive surface of the printing drum.It is hypothesized that the oxidized imaging oil may absorb moisturewhich alters the surface conductivity of the photosensitive surface ofthe printing drum. As a result of the oxidized imaging oil, the printagent moves or roams over the surface which causes print inaccuraciesand severe print quality (PQ) effects over time.

In various LEP printing systems, the oxidized imaging oil may also causedamage to the sensitive intermediate member. Regular replacement of thephotosensitive surface of the drum or the damaged intermediate membercan, however, be undesired from an economic point of view.

Empirical tests have shown that heating up the photosensitive surface ofthe printing drum to a temperature higher than 80° C. significantlyimproves PQ. It is hypothesized that temperatures higher than 80° C.evaporate the moisture of the oxidized imaging oil attached to thephotosensitive surface of the printing drum. The drying of the oxidizedimaging oil therefore weakens its adherence to the photosensitivesurface and thus enables its removal from the latter. Another hypothesisis that heating the oxidized imaging oil enriches the latter with oxygenwhich enables stronger OH-connections with a removal medium and therebyallows easier removal of the oxidized imaging oil layer.

“Photosensitive surface” is to be understood herein as a surface whichmay be partially charged or discharged when exposed to light. It is alsocapable of holding the charge when in the dark. Photosensitive surfacesmay comprise amorphous silicon, organic photo conductor (OPC), inorganicphoto conductor, photo conductive polymers, selenium or any type ofother photoconductive surface.

FIGS. 1 - 13 show a printing drum of a LEP printing system and relatedmethods wherein like reference numerals correspond to the samecomponents. Now referring to FIG. 1 which shows a perspective view of aprinting drum 100, wherein the printing drum 100 has been cut-open toallow a look inside the printing drum 100.

The printing drum 100 comprises a photosensitive surface 102. Thephotosensitive surface 102 may completely enclose the cylindric surfaceof the printing drum 100 with exception of the lateral sides. In anotherexample, the photosensitive surface 102 may cover the cylindric surfaceof the printing drum 100 in part.

Further, the printing drum 100 comprises a plurality of heating pads 101and a controller (not shown). The controller is electrically coupled tothe plurality of heating pads 101 and is to control independently atleast two or up to all of the plurality of heating pads 101 such thatthe photosensitive surface of the printing drum 100 is heated to atemperature having a predetermined temperature distribution. Theplurality of heating pads 101 can be combined into groups, with thegroups being controlled independently of one another to achieve thepredetermined temperature distribution.

In various LEP printing system, the predetermined temperaturedistribution of the photosensitive surface 102 of the printing drum 100may depend on development of the print agent and the process theprinting system is to perform. Herein, the controller may control thetemperature distribution of the photosensitive surface for at least fourdistinct processes of the LEP printing system accordingly which aredescribed hereinafter in more detail.

The predetermined temperature distribution may describe a temperaturedistribution on the surface of the printing drum 100 along thelongitudinal axis of the printing drum 100, in circumferential directionof the printing drum 100 or in any combination of these. The temperaturedistribution may be constant over the surface of the printing drum 100.The controller is to control the heating pads such that thepredetermined temperature distribution is achieved and maintained on thesurface of the printing drum 100, for instance by balancing heat lossesto the environment or to the end caps of the printing drum 100. Suchheat losses may be non-uniform along the photosensitive surface. Also,the controller is to control the heating pads such that thephotosensitive surface of the printing drum may be based on a format ofa printing job. The controller may heat a certain area of thephotosensitive surface which corresponds to the height and width of aprinting job format.

During a ready-to-print process, the controller is to control theplurality of heating pads such that the photosensitive surface is heatedto a printing temperature from e.g. ambient temperature. Theready-to-print process may be designated to reach the point in time forthe printing to start within a short time and is particularly suitablefor e.g. starting the printing drum of a LEP printing system after abreak or standby. The printing temperature may be a temperature in arange between 30 and 50° C., in particular between 35 and 45° C., moreparticular between 38 and 42° C. In other examples, the printingtemperature may be in a range between 40 and 49° C., in particularbetween 43 and 48° C. In yet another example, the printing temperaturemay be in range between 30 and 39° C., more particular in a rangebetween 31 and 34° C. In another example, the printing temperature is40° C. Various LEP printing system have a constant printing temperature.

During a quality enhancing process, the photosensitive surface has atemperature higher than 80° C. The print quality enhancing process maybe performed between a time range of 30 minutes and 6 hours. In someexamples, a temperature for the quality enhancing process may be in atemperature range between 90 and 110° C., in particular between 95 and105° C., more particular between 98 and 102° C. In another example, thetemperature for the quality enhancing process temperature may be in arange between 80 and 90° C., more particular between 84 and 89° C. Inyet another example, the print quality enhancing temperature may be in atemperature range between 110 and 130° C., in particular between 115 and125° C.

During a press priming process the photosensitive surface has atemperature higher than 80° C. to heat an intermediate member of the LEPprinting system. The intermediate member may be a belt which transfersthe print image to the substrate. By supporting heating of theintermediate member with the printing drums, the startup time of a LEPsystem may decrease. For press priming, the intermediate member isselectively engaged with the printing drum to enable heat transfer. Insome examples, the temperature for the press priming process may be in atemperature range between 90 and 110° C., in particular between 95 and105° C., more particular between 98 and 102° C. In another example, thetemperature for the press priming process temperature may be in a rangebetween 80 and 90° C., more particular between 84 and 89° C. In yetanother example, the press priming temperature may be in a temperaturerange between 110 and 120° C. In some LEP printing systems, thephotosensitive surface 102 heats the intermediate member such that atemperature equilibrium between the surface 102 and the intermediatemember may develop. Other LEP printing systems may provide an additionalheating element and the photosensitive surface 102 of the printing drum100 may support the additional heating element in heating theintermediate member during the press priming process as will bedescribed hereinafter. In some LEP printing systems, a sensor may sensethe temperature of the intermediate member and may provide feedback tothe controller. In other LEP printing systems, the control mechanism isbased on empirical data.

In some examples, the controller can control various components andoperations of the printing drum 100 to facilitate the processing andprinting as generally described herein, such as controllably heating thephotosensitive surface of the printing drum. In addition, the controllermay also communicate with further components of the LEP printing system.An example controller may include a processor (CPU) and a memory. Thecontroller may additionally include other electronics (not shown) forcommunicating with various components of the printing drum as well asthe LEP printing systems.

In one example, the controller is to control the plurality of heatingpads without feedback about the actual temperature of the heating padsor the photosensitive surface, based on empirical data prestored in thecontroller. In another example, the controller is to control theplurality of heating pads based on temperature feedback at least fromone of the plurality of heating pads and the photoconductive surface.

The plurality of heating pads 101 may be arranged along the longitudinalaxis of the printing drum 100, parallel to the longitudinal axis of theprinting drum 100, enclosing an angle with the longitudinal axis of theprinting drum 100, in circumferential direction of the printing drum 100or in any combination of these. The shape of an individual heating padmay be formed in circular, triangular, rectangular, polygonal,trapezoidal, or another shape. The height of the heating pads may berather small compared to their two-dimensional shape. In some examples,the plurality of heating pads 101 is arranged to cover a surface of theprinting drum 100 completely. In another example, the individual heatingpads of the plurality of heating pads 101 are distributed over at leastone distinct areas of the surface of the printing drum and, thus, coverits surface in part. In one example, the individual heating pads may bearranged physically adjacent to each other. In another example, theindividual heating pads 101 may be arranged spaced apart from eachother.

The printing drum 100 may comprises a hollow cylindrical element havingan inner and an outer surface. The printing drum 100 may be comprise afirm surface material and rotatably suspended on one or both lateralends within the LEP printing system. The photosensitive surface 102 ofthe printing drum 100 may comprise amorphous silicon or organicphotoconductor and the plurality of heating pads 101 may be mounted tothe inner surface of the hollow cylindrical element.

In one example, the plurality of heating pads 101 is arranged to theinner surface of the printing drum 100. The plurality of heating pads101 may be arranged with a heat-conductive adhesive to the printingdrum. In an example printing drum 100, the plurality of heating pads 101may be electrically and optically insulated and liquidly sealed fromother subsystems of the LEP printing system to avoid unfavorableinterferences with these subsystems.

In various LEP printing systems, the plurality of heating pads 101 maycomprise any of a rod heater, a film heater, a heating coil or a radiantheater. In another LEP printing systems, the plurality of heating pads101 may comprise any other suitable heater which does not interfere inan unnecessary manner with any other subsystems of the LEP printingsystem.

FIGS. 2 and 3 each show an example of the printing drum 100 as describedherein. In FIG. 2 , similar to FIG. 1 , a layer of the plurality ofheating pads 101 is mounted to the inner surface of printing drum 100which comprises a photosensitive surface 102.

In FIG. 3 , a layer of the plurality of heating pads 101 is mountedbetween the outer surface of a cylindrical element 301 of the printingdrum 100 and the photosensitive surface 102 of the printing drum. Inthis example, the photosensitive surface 102 of the printing drum 100may comprise a photo imaging plate (PIP) foil. Another example printingdrum may comprise two or more layers of the plurality of heating padsand thus different sandwich structures with the cylindrical element andunderneath the photosensitive surface 102 of the printing drum 100.

FIGS. 4 a - 4 c show further examples of the printing drum 100 asdescribed herein. The printing drum 100 comprises a mounting element 401on which the hollow cylindrical element of the printing drum 100 will beplaced. The plurality of heating pads 101 is arranged on the mountingelement such that heat is exchanged with the inner surface of the hollowcylindrical element to heat the photosensitive surface 101 of theprinting drum 100.

In particular, FIG. 4 a shows a circumferential layer of the pluralityof heating pads mounted to the mounting element 401. The mountingelement 401 may be a rod, a shaft, or any other kind of elongatedelement. The mounting element 401 may be attached to a suspension 402with one of its lateral ends. In another example, the mounting elementmay be attached to a suspension with both of its lateral ends. Themounting element may be rotatably attached to the suspension 402 and maybe connected to a drive which rotates the mounting element relative tothe suspension 402. In another example, the mounting element may befixed and the layer of the plurality of heating pads may be rotatablyattached to the mounting element and may be connected to a drive whichrotates the plurality of heating pads.

FIGS. 4 b and 4 c show the mounting process of the printing drum 100 tothe mounting element and the layer of the plurality of heating pads. InFIG. 4 b , the printing drum 100 is mounted to the mounting element 401in part, whereas FIG. 4 c shows the printing drum 100 mounted completelyon the mounting element 401 and over the layer of the plurality ofheating pads ready for use within a LEP printing system.

In one example, both, the mounting element and the plurality of heatingpads may be fixed while the hollow cylinder of the printing drum 100 isrotatably mounted to the mounting element and, thus, rotated relative tothe mounting element and the layer of the plurality of heating pads.

In various LEP printing systems, the mounting element 401, the layer ofthe plurality of heating pads and the hollow cylindric element may bearranged physically adjacent to each other. In another LEP printingsystems, the mounting element, the plurality of heating pads and thehollow cylindric element may be arranged apart from each other therebyenclosing spaces. In the latter system, these spaces in may be filledwith a heat-conducting medium.

FIG. 5 shows another example of the printing drum 100 as describedherein which comprises a temperature sensor 501 (schematically shown).The temperature sensor 501 is electrically coupled with the controller502 to sense the temperature distribution of the photosensitive surface102 and to feedback the temperature distribution to the controller. Thecontroller is to control the heating pads 101 independently in responseto the sensed temperature distribution. In one example, the temperaturesensor 501 may be an infrared camera. In another example, thetemperature sensor 501 may be resistance based or semiconductor based.In some examples, the temperature sensor 501 may sense the temperaturedistribution along the entire length of the printing drum 100. In otherexamples, the temperature sensor 501 may sense the temperaturedistribution where the heating pads are arranged.

FIG. 6 shows an example of the printing drum 100 wherein the controlleris electrically connected to the plurality of heating pads via arotating electrical connection 601. The rotating electrical connectionmay comprise any of brush-ring connection and a slip-ring connection. Inanother example, the controller is connected to the plurality of heatingpads wirelessly to control power outtake from a main power supply. Eachindividual heating pads may comprise a wireless interface to receivesignals. In another example, the plurality of heating pads may comprisea wireless interface to receive signals. In yet another example, theheating drum comprises an arrangement for wireless power transfer to theplurality of heating pads.

In a further example, an electrical circuit connecting the plurality ofheating pads to the controller may be designed to include electricalcomponents to support the predetermined temperature distribution e.g. bygenerating more heating power towards the lateral ends of the printingdrum.

Various LEP printing systems may comprise at least one printing drum asdescribed herein. Other LEP printing system may comprise a number ofprinting drums which corresponds to the number of printing colorsprovided for printing.

Now turning to FIG. 7 which shows an example LEP printing system 700.The LEP printing system 700 comprises an intermediate member 701 and twoprinting drums 100 a and 100 b. The printing drums comprise aphotosensitive surface 102, a heating device 702 and a controller (notshown) which is electrically coupled with the heating device 702. Thecontroller is to control the heating device 702 such that thephotosensitive surface is heated to a press priming temperature higherthan 80° C. to heat the intermediate member during the press-primingprocess. The printing drums 100 a, 100 b are arranged to be selectivelyengaged with the intermediate member 701. In FIG. 7 , printing drum 100a is selectively engaged with the intermediate member 701, whileprinting drum 100 b is selectively disengaged from the intermediatemember 701. When engaged with the intermediate member, the printingdrums may transfer heat to the intermediate member

In one LEP example, “engage” means physical contact between the printingdrum and the intermediate member. In this case, heat may be transferredby heat conduction through physical contact between the printing drum100 and the intermediate member 701. Also, a print image may betransferred by physical contact from the photosensitive surface 102 ofthe printing drum 100 to the intermediate member 702. In another LEPprinting system, “engage” allows a specific distance between theprinting drum 100 and the intermediate member 701. In this case, heatmay be transferred, for example, by heat radiation from the printingdrum 100 to the intermediate member 701. Also, a print image may betransferred by means of an electrical field between the photosensitivesurface 102 of the printing drum and the intermediate member 701. Incontrast, “disengage” means no interaction between the printing drum 100and the intermediate member 710.

In various LEP printing system, an engaging mechanism (not shown) may beprovided to engage the printing drum 100 with the intermediate member701. Such an engaging mechanism may either engage a moveable mountedprinting drum with the static intermediate member 701 or a printing drum100 with its longitudinal axis statically mounted and a moveable mountedintermediate member 701. In one example, the controller 502 may controlthe engaging mechanism. In another example, the controller 502 maycommunicate with the other subsystems of the LEP printing system 700 tocoordinate the heating processes with the engaging mechanism.

In various LEP printing system the heating device may comprise aplurality of heating pads and the controller is electrically coupledwith the plurality of heating pads to control the temperature of theheating pads independently such that the photosensitive surface isheated to a determined temperature. This predetermined temperature ofthe photosensitive surface 102 as well as the position of the printingdrum 100 with respect to the intermediate member 701 may depend on theprocess that is being performed. As described herein, the predeterminedtemperature has to be in a temperature range between 30° C. and 50° C.during a printing process or a ready-to-print process. During a printquality enhancing process, the temperature has to be higher than 80° C.to enhance the print quality of the photosensitive surface 102. Theprint quality enhancing temperature may be between 90 and 110° C. The atleast one printing drum is selectively disengaged from the intermediatemember during the ready-to-printing process and the print qualityenhancing process whereas it is selectively engaged with theintermediate member during the printing process.

In various LEP printing systems, the heating device 702 may comprise anyof a rod heater, a film heater, a heating pad, a heating coil or aradiant heater. In another LEP printing systems, the heating device 702may comprise any other suitable heater which does not interfere in anunnecessary manner with any other subsystems of the LEP printing system.

FIG. 8 shows a simplified front view of an example LEP printing system800 with an example printing drum 100 as described herein. The LEPprinting system 800 further comprises the intermediate member 701 whichis arranged to selectively engage with the printing drum 100. The LEPprinting system may further comprise a cleaning station 801. Thecleaning station 801 may be arranged to mechanically clean thephotosensitive surface of the printing drum 100 by exposing it to anelectrically neutral soft plastic blade and rotating sponge after theprint image has been transferred to the intermediate member. Thereby,remaining toner and/ or ink may be mechanically removed from thephotosensitive surface of the printing drum 100.

The LEP printing system 800 may further comprise a charging unit 802which may deposit a substantially uniform static charge on the exteriorof the photosensitive surface of the printing drum 100. In someexamples, the charging unit 802 may apply a corona discharge onto thephotosensitive surface. The photosensitive surface is then exposed tolight by a writing head 803 to selectively discharge pixels on thephotosensitive surface of the printing drum 100. This results in alatent electrostatic image on the photosensitive surface of the printingdrum.

Various LEP printing systems 800 may comprise a print agent applicator804. The print agent applicator, for instance a binary ink developer(BID) may develop and supply electrostatic ink. Also, an electrometer805 to measure the potential of the photosensitive surface may becomprised in an example LEP printing system 800.

The LEP printing system 800 may also include a print transfer erase(PTE) unit 806 to erase the electrostatic potential from thephotosensitive surface by exposing it to light before the print image istransferred to the intermediate member 701. Thereby, print qualityissues at a backing roller 807 are avoided. The backing roller 807squeezes the intermediate member 701 against the photosensitive surfaceof the printing drum 100 to transfer the print image to the intermediatemember 701. The intermediate member 701 then transfers the print imageto substrate.

Some print processes are performed with a number of printing systems 800that are connected by one intermediate member 701. Each printing system800 may apply a specific print agent to the intermediate member 701thereby forming one layer of the print image. In one example, the numberof printing systems 800 may correspond to the number of differentlycolored print agents provided in the print process.

Example methods of heating the photosensitive surface of a printing drumin a liquid electrophotographic printing system are shown in FIGS. 9 -13 . The methods may be performed by controller 502. The methods may beapplied to any of the example printing drums described above withrespect to FIGS. 1-8 .

Now turning to FIG. 9 which shows a method 900. Method 900 comprisesheating the photosensitive surface 102 with a heating device mounted tothe printing drum to a temperature higher than 80° C. during at leastone of a print quality enhancing process to enhance the print quality ofthe photosensitive surface and a press priming process in block 901. Thecontroller is to control the heating pads such that the temperaturehigher than 80° C. occurs in non-printing mode and is avoided during theprinting process and the ready-to-print process.

In FIG. 10 , a further example method 1000 for heating thephotosensitive surface 102 is shown. Method 1000 comprises, in block901, the method 900 and, in block 1001, additionally heating thephotosensitive surface 102 with the heating device, which comprises aplurality of heating pads, to a temperature having a predeterminedtemperature distribution. As described herein, the temperaturedistribution may be uniform or non-uniform and depending on the variousprocesses of the LEP printing system.

FIG. 11 shows a further example method 1010 for heating thephotosensitive surface 102 which comprises block 901. When block 901 isperformed within a press priming process, wherein the intermediatemember is heated to its operating temperature during a printing process,the controller may control the heating device such that the heatingdevice supports an additional heating element of the LEP printingsystem. The controller may control the heating device such that it stopsat a certain point in time. The point in time is determined such that itleaves sufficient time for the photosensitive surface to cool down tothe printing temperature for the printing process. The heating devicemay be stopped before the intermediate member has reached its operatingtemperature. The point in time is also determined such that theadditional heating element of the LEP printing system may compensate forthe remaining temperature gap of the intermediate member to itsoperating temperature.

The result is that the photosensitive surface and the intermediatemember reach their respective temperature for printing and operating atthe same time. The additional heating element of the LEP system maycomprise at least one fan heater. Thus, during the press primingprocess, the heating device may support an additional heating element ofthe LEP system in heating the intermediate member to its operatingtemperature. Above-described temperature ranges for the press primingtemperature of the photosensitive surface may also apply for thetemperature of the intermediate member for operating. Thus, theintermediate member may have a temperature higher than 80° C., inparticular any of the above-described temperature ranges, duringoperating within the LEP printing system.

Method 1010 further comprises in block 1011 heating the photosensitivesurface to a printing temperature in a temperature range between 30° and50° C. during at least one of a ready-to-print process and a printingprocess.

FIG. 12 shows a further example method 1020 for heating thephotosensitive surface which comprises, in addition to block 901 withmethod 900, a block 1021 of selectively engaging the printing drum withan intermediate member of the liquid electrophotographic printing systemduring a printing process and heating, by means of the heating device ofthe printing drum, the intermediate member during the printing process..

A further example method 1030 for heating the photosensitive surface 102is shown in FIG. 13 . The method 1030 comprises, in addition to block901 with method 900, a block 1031 of selectively disengaging theprinting drum from an intermediate member of the liquidelectrophotographic printing system during the print quality enhancingprocess in block 1031.

FIG. 14 shows another example method 1040 for heating the photosensitivesurface 102. Method 1040 comprises heating the photosensitive surface toa printing temperature in a temperature range between 30° and 50° C.during at least one of a ready-to-print process and a printing processin block 1041. Method 1040 may be performed after a break, standby, oranytime when the printing drum has ambient or colder temperature. Method1040 may be performed by itself or in combination with any other ofmethods 900, 1000, 1010, 1020 or 1030.

The present disclosure is described with reference to flow charts andblock diagrams of the method, devices and systems according to examplesof the present disclosure. Although the flow diagrams described aboveshow a specific order of execution, the order of execution may differfrom that which is depicted. Blocks described in relation to one flowchart may be combined with those of another flow chart. It shall beunderstood that various blocks in the flow charts and block diagrams, aswell as combinations thereof, can be realized by the controller.

While the method, apparatus and related aspects have been described withreference to certain examples, various modifications, changes,omissions, and substitutions can be made without departing from thespirit of the present disclosure. It should be noted that theabove-mentioned examples illustrate rather than limit what is describedherein, and that those skilled in the art will be able to design manyalternative implementations without departing from the scope of theappended claims. Features described in relation to one example may becombined with features of another example.

What is claimed is:
 1. A printing drum for a liquid electrophotographicprinting system, the printing drum comprising: a photosensitive surface,a plurality of heating pads mounted to the printing drum, and acontroller electrically coupled with the plurality of heating pads,wherein the controller is to control the heating pads independently suchthat the photosensitive surface of the printing drum is heated to atemperature having a predetermined temperature distribution.
 2. Theprinting drum according to claim 1, further comprising a temperaturesensor electrically coupled with the controller to sense the temperaturedistribution of the photosensitive surface, wherein the controller is tocontrol the heating pads independently in response to the sensedtemperature distribution.
 3. The printing drum according to claim 1,wherein the printing drum comprises a hollow cylindrical element havingan inner and an outer surface, wherein the photosensitive surface of theprinting drum comprises amorphous silicon, and wherein the plurality ofheating pads is mounted to the inner surface of the hollow cylindricalelement.
 4. The printing drum according to claim 1, wherein the printingdrum comprises a hollow cylindrical element having an inner and an outersurface, and a mounting element on which the hollow cylindrical elementis mounted to; wherein the photosensitive surface of the printing drumcomprises at least one of amorphous silicon and organic photoconductor,and wherein the plurality of heating pads is arranged on the mountingelement such that heat is exchanged with the inner surface of the hollowcylindrical element.
 5. The printing drum according to claim 1, whereinthe printing drum comprises a cylindrical element having an outersurface, wherein the photosensitive surface of the printing drumcomprises a photo imaging plate foil, and wherein the plurality ofheating pads is mounted between the outer surface of the cylindricalelement and the photosensitive surface.
 6. The printing according toclaim 1, wherein the controller is to control the plurality of heatingpads such that the photosensitive surface is heated to a print qualityenhancing temperature higher than 80° C. during at least one of a printquality enhancing process to enhance the print quality of thephotosensitive surface and a press priming process.
 7. The printing drumaccording to claim 1, wherein the controller is further to control theplurality of heating pads such that the photosensitive surface is heatedto a printing temperature in a temperature range between 30° and 50° C.during at least one of a ready-to-print process and a printing process.8. The printing drum according to claim 1, wherein the controller iselectrically connected to the plurality of heating pads via a rotatingelectrical connection, wherein the rotating electrical connectioncomprises any of brush-ring connection and a slip-ring connection.
 9. Aliquid electrophotographic printing system, comprising an intermediatemember, at least one printing drum, comprising: a photosensitivesurface, a heating device, and a controller electrically coupled withthe heating device; wherein the at least one printing drum isselectively engaged with the intermediate member during a press-primingprocess and wherein the controller is to control the heating device suchthat the photosensitive surface is heated to a press priming temperaturehigher than 80° C. to heat the intermediate member during thepress-priming process.
 10. The liquid electrophotographic printingsystem according to claim 9, wherein the heating device comprises aplurality of heating pads and the controller is electrically coupledwith the plurality of heating pads to control the temperature of theheating pads independently such that the photosensitive surface isheated to the printing temperature in a temperature range between 30° C.and 50° C. during a printing process or a ready-to-print process, and toa print quality enhancing temperature higher than 80° C. during a printquality enhancing process to enhance the print quality of thephotosensitive surface; wherein the at least one printing drum isselectively disengaged from the intermediate member during theready-to-printing process and the print quality enhancing process.
 11. Amethod to heat a photosensitive surface of a printing drum in a liquidelectrophotographic printing system, comprising: - heating thephotosensitive surface with a heating device mounted to the printingdrum to a temperature higher than 80° C. during at least one of a printquality enhancing process to enhance the print quality of thephotosensitive surface and a press priming process.
 12. The methodaccording to claim 11, further comprising heating the photosensitivesurface with the heating device, which comprises a plurality of heatingpads, to a temperature having a predetermined temperature distribution.13. The method according to claim 11, further comprising heating thephotosensitive surface to a printing temperature in a temperature rangebetween 30° and 50° C. during at least one of a ready-to-print processand a printing process.
 14. The method according to claim 11, furthercomprising selectively engaging the printing drum with an intermediatemember of the liquid electrophotographic printing system during aprinting process and heating, by means of the heating device of theprinting drum, the intermediate member during the printing process. 15.The method according to claim 11, further comprising selectivelydisengaging the printing drum from an intermediate member of the liquidelectrophotographic printing system during the print quality enhancingprocess.